Yes, but half the ball isn't a "fine margin". Hawkeye ball-tracking technology is trustworthy to within about 4 millimetres, and given that a cricket ball is rather wider than 4mm you ought to treat an about half-ball impact as hitting.
At the very least, if the decision to review leads to an umpire's call it seems harsh to take away a review. If the decision were initially not out and the fielding team reviews and gets an umpire's call, then if the Umpire had agreed with them in the first place the batsman would have been out. So Umpire's calls are double-whammies. Not only do you not get the wicket when you might have, but you lose a review.
It's critical later down the line, as Smith was out plumb a few overs back and not given, with no reviews left. Not sure the technology rules are correct as they stand.
Australia and Smith have survived, anyway, and they have reached 208/3.